1. Field of the Invention
The present invention relates to a magnetic head including a magneto-resistance effect element and side shields used in hard disc drives (HDD).
2. Description of the Related Art
A magneto-resistance effect element (for example, a TMR (tunnel magneto-resistance effect) element) used in HDD readers is configured of a multilayer film in a spin valve structure consisting of a free layer of which the magnetization direction changes with respect to the external magnetic field, a pinned layer of which the magnetization direction is fixed with respect to the external magnetic field, a spacer layer situated between the free layer and the pinned layer, a pinning layer for fixing the magnetic field of the pinned layer, and the like. The magneto-resistance effect element is interposed between a pair of shields that are situated on both sides in the lamination direction (down track direction) of the layers configuring the magneto-resistance effect element and that also serve as electrodes. The down track direction is the direction along the magnetic recording tracks of a recording medium (HD) read by the magneto-resistance effect element. The direction perpendicular to and crossing the down track direction is the cross track direction.
For example, the magnetic head disclosed in U.S. Pat. No. 7,692,901B1 is provided with side shields on both sides of the magneto-resistance effect element in the direction perpendicular to the lamination direction (the cross track direction). The side shields include a soft magnetic substance and also function as bias magnetic field application layers for aligning the magnetization direction of the free layer, particularly when no external magnetic field is applied. The pair of side shields is magnetically coupled to one of a pair of shields (for example, the upper shield situated above in the lamination direction). Moreover, an anisotropy-application layer (for example, an IrMn layer) is disposed adjacent to the shield magnetically coupled to the side shields. The anisotropy-application layer imparts exchange anisotropy to the adjacent shield to magnetize it in a desired direction (one way in the cross track direction). Then, the pair of side shields magnetically coupled to this shield is magnetized in the same direction as the shield. As described above, the free layer of the magneto-resistance effect element surrounded by the shield and the side shields magnetized in the same direction has a magnetization direction aligned in the cross track direction when no external magnetic field is applied.
A reader having the above side shields and anisotropy-application layer has a configuration in which the magneto-resistance effect element, the pair of shields, and the anisotropy-application layer are stacked, and therefore has a large dimension in the down track direction, whereby the read gap is increased.
Moreover, in order to improve the area density capacitance (ADC) in recent HDDs, multi-reader heads having multiple readers have been developed. US2011/0216432A1 discloses a configuration in which two independent readers comprising a magneto-resistance effect element are each interposed between a pair of shields and are stacked and separated by an insulating layer. When such multiple readers independent from each other are stacked and separated by an insulating layer, and each reader consists of a TMR element or GMR element of the CPP (current perpendicular to plane) type in which the current flows in the direction perpendicular to the main surface of the layers, the positional relationship between the reader situated below and the reader situated above and the accuracy of width and height of the readers are important, and precise processing and control is required. Particularly, it is important to reduce the reader-reader separation (RRS), which affects the accuracy of reading of adjacent tracks, as much as possible, which is a major key point to obtain the features of a multi-reader head. Further, the RRS is the distance in the lamination direction between the centerlines of the free layers of the magneto-resistance effect elements of adjacent readers in the lamination direction.
In a multi-reader head in which multiple readers are stacked as described above, it is required to reduce the RSS to, for example, several tens of nm. As shown in FIGS. 1a and 1b, when a magneto-resistance effect element V and side shields 2 situated on both sides of a reader R1 situated below are interposed between a lower shield S1 and an upper shield S2, and a magneto-resistance effect element V and side shields 2 situated on both sides of a reader R2 situated above are interposed between a lower shield S3 and an upper shield S4, the upper shield S2, the lower shield S3, an inter-element insulating layer 9, and an anisotropy-application layer 8 (IrMn film) are included between the magneto-resistance effect element V of the reader R1 and the magneto-resistance effect element V of the reader V2. If the shields S2 and S3 are excessively thin in order to reduce the RRS, the SN ratio problematically drops because the shields S2 and S3 also serve as the electrodes of the readers R1 and R2. Moreover, there is a limit on reducing the thickness of the inter-element insulating film 9 in order to ensure the withstand voltage of the readers R1 and R2. Thus, there is a need for some other measure to reduce the RRS.
Throughout this specification, regardless of the orientation of the magnetic head in use, the lamination direction of the layers of the magneto-resistance effect element is referred to as the vertical direction, and one side in the lamination direction is referred to as “upper” and the other side is referred to as “lower.” As an example, the positional relationship between “upper” and “lower” is defined so that the pinning layer side of a magneto-resistance effect element is referred to as “lower” and the free layer side is referred to as “upper.” This lamination direction is equal to the lamination direction of multiple readers of a multi-reader head, and generally the reader formed earlier in the production process of a multi-reader head is “a lower reader” and the reader stacked and formed later is “an upper reader.” Moreover, the lamination direction is equal to the down track direction. The terms “upper” and “lower” are used based on the above definition also with regard to various members other than the magneto-resistance effect element and readers.